Understanding SCADA and data loggers

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The quality of observational data directly affects

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the accuracy of a network model,

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inaccurate missing or misunderstood data drastically

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changes a model's configuration and calibration

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SCADA

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or supervisory control.

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And data acquisition refers to the system of computers

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and instruments that controls or monitors a process.

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Keta can refer to a system that monitors an entire treatment

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works or it can refer to a simple pump control.

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The primary benefit of SK systems is the ability to

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control or monitor a plan remotely instead of on site.

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Telemetry refers to any data collected by a SCADA

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system

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once collected.

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This data is often communicated from the site to a centralized data storage server

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because SK systems can also control equipment.

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It is essential that the rules provided to the system

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are matched in the model as closely as possible.

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Logic is implemented via programmable logic

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controllers or plc's which determine what actions

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the system should take based on inputs and rules provided to it.

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Another important tool to consider when working

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with network modeling is the data logger.

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Data loggers are portable low cost battery powered devices that are often

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used within the water distribution network to record flow and pressure.

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Data loggers are typically less reliable than SCADA

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for data delivery.

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In the past,

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many data loggers stored data in such a way

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that manual downloading was required with limited storage.

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Now,

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almost all data loggers are cloud based or they send data via cellular networks.

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Data loggers are mostly permanently installed

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devices such as district flow meters,

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but some are lift in shift devices that can be

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moved around for a specific goal such as network calibration

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understanding data is critical to using it in the correct way.

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In the water industry.

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Data is typically used as a time series which means a property

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is tracked over time at a given interval called a sample rate.

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This sample rate is often 15 minutes.

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Although some sources record an instantaneous

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sample while others will be averaged,

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accurate pressure measurements are also critical to network modeling,

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especially when calibrating networks or isolating head loss.

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An accurate pressure measurement depends upon the

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accuracy of the sensor which is specified

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by the manufacturer as a percentage error of a sensor's full scale accuracy.

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Another consideration is whether the sensor records absolute or gauge pressure.

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When measuring an enclosed pressurized system,

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emphasis is placed on the pressure of the fluid relative to the sampling point.

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Because of this,

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most pressure sensors used are gauge pressure

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which records zero at or near atmospheric pressure

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because atmospheric pressure varies by location and altitude devices that

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are zeroed in different places may produce inconsistent results.

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Finally, there are two types of signals from flow meters

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pulses and 4 to 20 milli

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ap

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signals.

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A 4 to 20 milli

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ap signal is generated by an electromagnetic flow meter

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typically at a treatment works or water distribution site

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pulses are typically obtained from bulk flow meters and customer meters.

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A pulse reports that a specific volume of

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water has passed through the meter since the

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last pulse which can limit their use when recording lower flows where 4 to 20 milli

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signals update at fixed intervals providing an accurate instantaneous flow rate.